An unusual adenosquamous carcinoma originating in the prostate of a 73-year-old man is described. The histological finding showed a well differentiated squamous cell carcinoma admixed in an adenocarcinomatous area. A transitional area of 2 carcinomatous elements was also noted. Seven months prior to the development of this lesion, a diagnosis of adenocarcinoma had been established by transurethral resection of the prostate and the patient had been treated with bilateral orchiectomy. This is the first case of adenosquamous carcinoma of the prostate reported in Korea. The pathogenesis and previous reports of this lesion will be discussed.